Silicon carbide wafer power modulation lift-off method, medium, and apparatus

Abstract

This invention relates to the field of silicon carbide wafer processing technology, specifically to a silicon carbide wafer power modulation stripping method, medium, and equipment. The method includes the following steps: setting a control program for the wafer size, specifically: determining the laser position by calculating the X and Y coordinates of the laser based on the laser processing time; analyzing power changes, setting a power range, calculating a power command based on the power range, and transmitting the power command to the dynamically modulated output voltage of a picosecond pulse laser. This invention reduces the temperature difference on the stripped surface, thereby significantly reducing residual thermal stress at the edges. The flatness of the modified layer obtained by laser stripping is better than before, and the wafer roughness after stripping is smaller, which can reduce material loss in subsequent grinding processes.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide wafer processing technology, and in particular to a silicon carbide wafer power modulation stripping method, medium, and equipment. Background Technology

[0002] Silicon carbide (SiC) possesses a large bandgap, a high critical breakdown electric field, high thermal conductivity, high electron mobility, and stable chemical properties, making it a leading representative of third-generation semiconductors. However, precisely because of its stable chemical properties, SiC also exhibits extremely high hardness and brittleness, making it a difficult material to process.

[0003] The traditional method for obtaining wafer substrates from SiC ingots is diamond wire cutting. This technology has low processing efficiency, high kerf loss, and causes environmental pollution. Furthermore, such contact processing can cause problems such as wafer cracking and residual stress, reducing its quality and lifespan. With the continuous advancement of laser processing technology for hard and brittle materials, ultrafast lasers are increasingly being applied in SiC wafer processing. Ultrafast lasers offer advantages such as high peak power, small heat-affected zone, non-contact processing, and easy precise control, providing an ideal solution for silicon carbide wafer substrate processing. Laser lift-off involves focusing the ultrafast laser inside the ingot, utilizing the interaction between the laser and the material to form a modified layer, reducing the internal bonding force of the crystal, and then using external force to achieve wafer separation.

[0004] However, when a laser acts on the interior of a SiC ingot, the difference in heat dissipation rates between the ingot's edge and center regions causes significant residual thermal stress at the material edges. This can lead to defects such as edge chipping when the wafer is peeled off using external force. Therefore, innovative processing techniques are urgently needed to balance the temperature field distribution of SiC ingots during laser processing. Summary of the Invention

[0005] The main objective of this invention is to provide a silicon carbide wafer power modulation stripping method, medium, and equipment, which aims to solve the technical problem that when laser stripping is used in the existing SiC wafer processing and production process, the difference in heat dissipation rate between the wafer edge and the center region will cause significant residual thermal stress at the material edge, resulting in defects such as edge chipping.

[0006] To achieve the above objectives, the present invention proposes a silicon carbide wafer power modulation stripping method, comprising the following steps: The wafer size setting control program is as follows: the position of the laser is determined by calculating the X and Y coordinates of the laser based on the laser processing time; the initial center of the circle is set as the origin of the coordinate system; positive and negative X coordinate values ​​are calculated based on the X coordinate; the initial laser displacement path is set from left to right; the X coordinate value of the laser is obtained by determining whether the current number of laser processing lines is odd or even; and the movement of the operation platform is controlled by the X coordinate value of the laser. The power variation is analyzed, the power range is set, the power command is calculated through the power range, and the output voltage of the pulse picosecond laser is dynamically modulated through the power command.

[0007] The silicon carbide wafer power modulation stripping method of the present invention is further improved in that, when calculating the X and Y coordinates of the laser based on the laser processing time, the laser energy is controlled between 0-7.5 μJ by controlling the laser output intensity, thereby determining the scanning speed of the picosecond pulse laser. And the displacement set on the Y-axis for each laser scan Assuming the current process is the first laser processing step... The line is initially set to the furthest distance from the center of the silicon carbide ingot to the edge. =5.0mm, =25 , =20mm / s: Y coordinate : ; X coordinate : .

[0008] A further improvement of the silicon carbide wafer power modulation stripping method of the present invention is that, before obtaining the power command through power range calculation, the current position of the laser emitted by the picosecond pulse laser is calculated from the center of the silicon carbide ingot. : .

[0009] A further improvement of the silicon carbide wafer power modulation stripping method of the present invention is that, when the power command is calculated through the power range, the distance between the current position of the laser emitted by the picosecond pulse laser and the center of the silicon carbide ingot is... Mapped to power instruction: ; in, For minimum power, This is the maximum power.

[0010] A further improvement of the silicon carbide wafer power modulation stripping method of the present invention is that, when processing only the edge of the silicon carbide ingot using a picosecond pulse laser, the laser emitted by the picosecond pulse laser exhibits a Gaussian curve growth, as expressed below: ; in: Parameters used to control the shape of the curve.

[0011] The silicon carbide wafer power modulation stripping method of the present invention is further improved in that, when dynamically modulating the output voltage, the output voltage increases as the laser point of action is farther from the center of the silicon carbide ingot on the operating platform, thereby increasing the laser energy; conversely, the output voltage decreases as the laser point of action is closer to the center of the silicon carbide ingot on the operating platform, thereby decreasing the laser energy.

[0012] In addition, the present invention provides a readable storage medium storing a computer program adapted to be loaded by a processor and executed as described above for the silicon carbide wafer power modulation stripping method.

[0013] In addition, the present invention also provides a computer device, the computer device including a memory and a processor, the memory storing a computer program, which, when executed by the processor, runs the silicon carbide wafer power modulation stripping method as described above.

[0014] The technical solution of the present invention has the following beneficial effects: The silicon carbide wafer power modulation lift-off method of this invention uses an algorithm to control a picosecond laser and an operating platform. A predetermined program calculates the possible X and Y coordinates of the current processing position of the laser spot, and then determines the accurate X coordinate by judging the parity of the current laser beam count. The power is determined by calculating the laser's distance from the center, thus achieving a variable power effect. This reduces the temperature difference on the lift-off surface, significantly reducing residual thermal stress at the edges. Compared to the lift-off surface quality under laser self-focusing, this method results in a smoother modified layer and lower wafer roughness, reducing material loss in subsequent grinding processes. Furthermore, this method significantly increases the processing speed and solves the technical problem in existing SiC wafer processing using laser lift-off methods where the difference in heat dissipation rates between the wafer edge and center causes significant residual thermal stress at the material edges, leading to defects such as edge chipping. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the specific implementation platform used in the silicon carbide wafer power modulation stripping method of the present invention; Figure 2 This is a schematic diagram of the edge chipping caused by residual stress in the edge region of a traditional laser-lifted wafer. Figure 3 A schematic diagram of the structure of the central region of a traditional laser lift-off wafer. Figure 4 This is a schematic diagram of the surface structure of a wafer lifted by a conventional constant-power laser. Figure 5 This is a schematic diagram of the surface structure of the silicon carbide wafer stripped by the silicon carbide wafer power modulation stripping method of the present invention; Figure 6 This is a diagram showing the internal temperature distribution of the wafer when it is stripped without using variable power. Figure 7 This is a diagram showing the internal laser power distribution of the silicon carbide wafer during wafer stripping using the silicon carbide wafer power modulation stripping method of the present invention. Figure 8 This is a power-distance relationship curve during wafer stripping using the silicon carbide wafer power modulation stripping method of the present invention; Figure 9 The Gaussian power modulation simulation curve is shown for the silicon carbide wafer power modulation stripping method of this invention.

[0017] Explanation of icon numbers: 1. Pulsed picosecond laser; 2. Attenuator; 3. Beam expander; 4. Dichroic beam splitter; 5. Plano-convex lens; 6. CCD; 7. Objective lens; 8. Operating platform; 9. Computer. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0020] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0021] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0023] When ultrafast lasers are applied to silicon carbide (SiC) ingots, the heat generated by the laser energy deposition is more difficult to dissipate in the central region of the ingot compared to the edge region due to differences in heat flux. This results in temperature gradient differences and cooling rate differences, leading to a sharp increase in steady-state thermal stress and transient shrinkage stress. Consequently, when external force is used for separation, the residual stress in the edge region of the SiC wafer can cause severe defects such as edge chipping. Figure 2 Edge areas and Figure 3 Comparison of the central region. Therefore, based on thermodynamic simulation analysis, this invention proposes a silicon carbide wafer power modulation stripping method. By modulating the laser power at different scanning positions, the temperature field imbalance between the edge and central regions of the processed SiC ingot is reduced, thereby reducing the residual stress in the edge region of the SiC ingot and improving the quality of the stripped SiC wafer.

[0024] The specific implementation platform of this invention includes components such as a picosecond laser 1, an attenuator 2, a beam expander 3, a dichroic beam splitter 4, a plano-convex lens 5, a CCD 6, an objective lens 7, an operating platform 8, and a computer 9. Figure 1 As shown. At the start of processing, the SiC ingot is placed on the operating platform 8. A laser beam is output from the picosecond laser 1 to the attenuator 2 (the attenuator 2 is used for later fine-tuning of the laser power). The laser beam is then magnified by the beam expander 3 to reduce the beam divergence angle, facilitating subsequent beam shaping. The laser beam is then reflected by the dichroic beam splitter 4 to the objective lens 7, which focuses the beam onto the SiC ingot on the moving platform. By adjusting the X, Y, and Z degrees of freedom of the operating platform 8, the laser is focused at a specific depth on the ingot for top-to-bottom scanning to form the modified layer. During processing, the scene being processed on the SiC ingot is reflected by visible light and imaged onto the CCD 6 by the dichroic beam splitter 4 and the plano-convex lens 5 to assist in focus adjustment. Simultaneously, the CCD 6 transmits the scene being processed to the computer 9, where algorithms analyze the processing conditions to control the laser output power. Finally, by applying mechanical stress, cracks are induced to propagate along the modified layer direction, causing the SiC ingot to peel off.

[0025] Specifically, this invention proposes a silicon carbide wafer power modulation stripping method. Through a pre-set program, laser power modulation technology is used to solve the problem of uneven temperature distribution of the modified layer of the silicon carbide ingot during stripping. Furthermore, it can calculate distances using different methods for silicon carbide ingots of different shapes, including the following steps: The wafer size setting control program specifically works as follows: The laser's position is determined by calculating its X and Y coordinates based on the laser processing time; the initial center is set as the coordinate origin; positive and negative X coordinate values ​​are calculated based on the X coordinates; the initial laser displacement path is set from left to right; the X coordinate value of the laser is obtained by determining whether the current number of laser processing passes is odd or even; and the movement of the operating platform 8 is controlled by the laser's X coordinate value. Specifically, the laser's X coordinate value is transmitted to the computer 9, which then controls the movement of the operating platform 8.

[0026] Preferably, when calculating the X and Y coordinates of the laser based on the laser processing time, the laser energy is controlled between 0 and 7.5 μJ by controlling the laser output intensity, thereby determining the scanning speed of the picosecond pulse laser 1. And the displacement set on the Y-axis for each laser scan Assuming the current process is the first laser processing step... The line is initially set to the furthest distance from the center of the silicon carbide ingot to the edge. =5.0mm, =25 , =20mm / s: Y coordinate : ; X coordinate : .

[0027] The power variation is analyzed, a power range is set, a power command is calculated based on the power range, and the output voltage of the picosecond laser 1 is dynamically modulated using the power command. Specifically, the power command is transmitted to computer 9, which then controls the dynamic modulation of the output voltage of the picosecond laser 1.

[0028] Preferably, before obtaining the power command through power range calculation, the current position of the laser emitted by the picosecond laser 1 from the center of the silicon carbide ingot is calculated. : .

[0029] The distance from the current position of the laser emitted by the picosecond laser 1 to the center of the silicon carbide ingot. Mapped to power instruction: ; in, To achieve minimum power, in this embodiment ; This is the maximum power.

[0030] Furthermore, for scenarios where only the edges of silicon carbide ingots need to be processed, when the edge of the silicon carbide ingot is processed only by the pulsed picosecond laser 1, the laser emitted by the pulsed picosecond laser 1 exhibits a Gaussian curve growth, as expressed below: ; in: Parameters used to control the shape of the curve. The larger the value, the faster the power increases near the center; The smaller the value, the slower the growth. Typically, a value is taken as... =5 can make the power at =0.5 is close to The processing power of this curve is almost entirely concentrated in the edge region, with almost no processing capacity in the center. Simulation results are as follows... Figure 9 As shown.

[0031] Application scenarios of Gaussian curve power modulation: Suitable for scenarios where efficient stripping or modification of the ingot edge region is required, while the central region requires minimal processing (center protection). Adjust parameters accordingly. This allows more than 90% of the energy to be concentrated in the 50%-100% ring region.

[0032] This method is suitable for situations where a modified layer is formed inside a wafer, requiring high edge energy to facilitate crack propagation.

[0033] The difference between Gaussian power modulation and linear growth: linear power modulation is suitable for situations where the power needs to be processed smoothly from the center to the edge to avoid local overheating or overcooling; Gaussian power modulation is suitable for situations such as edge strengthening processing of ingots and center protection.

[0034] Preferably, when dynamically modulating the output voltage, the output voltage increases as the laser point of action is farther from the center of the silicon carbide ingot on the operating platform 8, resulting in increased laser energy; conversely, the output voltage decreases as the laser point of action is closer to the center of the silicon carbide ingot on the operating platform 8, resulting in decreased laser energy.

[0035] In addition, the present invention provides a readable storage medium storing a computer program adapted to be loaded by a processor and executed as described above for the silicon carbide wafer power modulation stripping method.

[0036] In addition, the present invention also provides a computer device, the computer device including a memory and a processor, the memory storing a computer program, which, when executed by the processor, runs the silicon carbide wafer power modulation stripping method as described above.

[0037] In the ingot peeling process, there is a significant difference in heat dissipation conditions between the edge and center regions. The edge, due to its contact with air, experiences a much higher heat dissipation rate than the center, leading to uneven thermal stress distribution, especially stress concentration at the edge. This residual thermal stress can easily induce brittle fracture of the edge material during separation along the pre-set continuous modified layer, resulting in problems such as edge chipping and increased surface roughness on the peeled surface.

[0038] The present invention designs a program based on the movement position of the laser on the crystal ingot surface and the change of laser power, thereby controlling the movement of the operating platform 8 in the X and Y directions and the power of the pulsed picosecond laser 1, so that the two cooperate with each other during the peeling process to ensure that the temperature gradient from the center to the edge of the modified layer is small during the peeling of the crystal ingot, thereby reducing the residual thermal stress at the edge.

[0039] By real-time detection of the distance between the laser's point of application and the center of the ingot, and dynamic modulation of the laser's output voltage based on this distance information, precise control of the laser output energy can be achieved. This energy distribution modulation can actively compensate for the thermal stress gradient caused by differences in heat dissipation conditions during the ingot peeling process, and can effectively suppress residual tensile stress caused by excessive heat dissipation in the edge region. Through this method, the probability of edge chipping during peeling is significantly reduced, and the quality of the peeled surface is improved, thereby greatly improving the quality of subsequent wafer processing. Using constant power (such as...) Figure 4 ) and modulation power (e.g. Figure 5 ) Surface condition after.

[0040] The simulation results are as follows, under the condition of constant power processing. Figure 4 and Figure 5 As shown, because the heat dissipation rate in the edge region is higher than that in the center region, while the heat conduction rate in the center region is relatively slower, heat accumulates in the center, resulting in a temperature distribution in the processing area that is high in the center and low around the edges.

[0041] Based on constant power simulation results, this application sets different variable power parameters for SiC ingots of different sizes, thereby applying lasers of different powers to different regions of the ingots. The simulation results are as follows: Figure 6 As shown.

[0042] Based on simulation results, after adopting power modulation technology, such as Figure 7 and Figure 8 As shown in the temperature distribution diagram, the red areas correspond to areas with higher temperatures, and the blue areas correspond to areas with lower temperatures, thus achieving differentiated temperature control between the center and edges of the SiC sample during the peeling process. By adjusting the laser output power according to the distance between the laser beam and the center of the SiC sample, the temperature non-uniformity caused by different heat dissipation conditions can be effectively compensated, thereby eliminating or significantly reducing the residual thermal stress in the SiC sample after peeling.

[0043] As can be seen, during the peeling process, the present invention precisely controls the laser output power through a pre-designed algorithm to achieve differentiated power processing of the laser at different locations of the silicon carbide ingot. This compensates for the temperature non-uniformity caused by the difference in heat dissipation rate between the center and the edge regions, thereby effectively suppressing the formation of excessive temperature gradient at the peeling interface, reducing or eliminating the residual thermal stress caused by it, and thus improving the surface quality of the wafer after peeling.

[0044] The above description is only a preferred embodiment of the present invention and does not limit the scope of the present invention. All equivalent structural transformations made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the protection scope of the present invention.

Claims

1. A method for power modulation stripping of silicon carbide wafers, characterized in that, Includes the following steps: The wafer size setting control program is as follows: the X and Y coordinates of the laser are calculated by the laser processing time to determine the position of the laser; the center of the circle is initially set as the origin of the coordinates, and positive and negative X coordinate values ​​are calculated according to the X coordinates. The initial laser displacement path is set from left to right. The X coordinate value of the laser is obtained by checking whether the current number of laser processing lines is odd or even, and the operation platform (8) is moved by controlling the X coordinate value of the laser. The power variation is analyzed, the power range is set, the power command is calculated through the power range, and the output voltage of the pulse picosecond laser (1) is dynamically modulated through the power command.

2. The silicon carbide wafer power modulation stripping method according to claim 1, characterized in that, When calculating the X and Y coordinates of the laser based on the laser processing time, the scanning speed of the picosecond pulse laser (1) is determined by controlling the laser output intensity to keep the laser energy between 0 and 7.5 μJ. And the displacement set on the Y-axis for each laser scan Assuming the current process is the first laser processing step... The line is initially set to the furthest distance from the center of the silicon carbide ingot to the edge. =5.0mm, =25 , =20mm / s: Y coordinate : ； X coordinate :

3. Then determine the specific coordinates of X: determine whether the line being processed is an odd or even number of lines. For time The coordinates of the laser on the scanning line. This is the time when the line started; Odd-numbered line coordinates: ; Even number of line coordinates: .

4. The silicon carbide wafer power modulation stripping method according to claim 2, characterized in that, Before obtaining the power command through power range calculation, calculate the current position of the laser emitted by the picosecond laser (1) from the center of the silicon carbide ingot. : 。 5. The silicon carbide wafer power modulation stripping method according to claim 3, characterized in that, When the power command is calculated through the power range, the current position of the laser emitted by the picosecond laser (1) is the distance from the center of the silicon carbide ingot. Mapped to power instruction: ； in, For minimum power, This is the maximum power.

6. The silicon carbide wafer power modulation stripping method according to claim 4, characterized in that, When processing only the edge of a silicon carbide ingot using a picosecond pulsed laser (1), the laser emitted by the picosecond pulsed laser (1) exhibits a Gaussian curve growth, as expressed below: ； in: Parameters used to control the shape of the curve.

7. The silicon carbide wafer power modulation stripping method according to claim 1, characterized in that, When the output voltage is dynamically modulated, the output voltage increases as the laser point is further away from the center of the silicon carbide ingot on the operating platform (8), resulting in increased laser energy; conversely, the output voltage decreases as the laser point is closer to the center of the silicon carbide ingot on the operating platform (8), resulting in decreased laser energy.

8. A readable storage medium, characterized in that, The readable storage medium stores a computer program adapted to be loaded by a processor and executed as the silicon carbide wafer power modulation stripping method according to any one of claims 1-6.

9. A computer device, characterized in that, The computer device includes a memory and a processor. The memory stores a computer program, which, when executed by the processor, performs the silicon carbide wafer power modulation stripping method according to any one of claims 1-6.

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